Asthma and Chronic Obstructive Pulmonary Disease Overlap: The Effect of Definitions on Measures of Burden.

Background: Although the overlap between asthma and COPD has been recognized for years this overlap has only recently been given a name, asthma-COPD overlap syndrome (ACOS), and better defined. Different definitions of the component diseases can affect prevalence and outcome measures of ACOS. Methods: We used data from the National Health and Nutrition Examination Survey (NHANES) from 2007-2012 to determine the population estimates of ACOS in U.S. adults using 2 different definitions of ACOS (ACOS1= self-reported COPD and current asthma; ACOS2 = spirometric-confirmed COPD [pre-bronchodilator FEV1/FVC < 70%] and current asthma) and to describe variation in other factors, such as lung function impairment and health care utilization, by ACOS definitions. Results: Among U.S. adults aged 20 and older, 1.6% had ACOS1, and 1.9% had ACOS2. Both case definitions were similar with regard to symptoms and impairment of lung function. ACOS1 individuals were more likely to have one or more overnight hospital stays relative to those with neither asthma nor COPD, (odds ratio [OR] 3.4, 95% confidence interval [CI] 2.5, 4.6) than ACOS2 (OR 1.6, 95% CI 0.9, 2.9). Conclusions: Different definitions of ACOS in population-based studies affect both estimates of disease prevalence and outcomes related to the disease. These definitions need to be carefully considered in the design of epidemiologic studies and clinical trials.